The NORSOK M-710 specification underlines the need for oilfield equipment OEMs to achieve higher levels of quality and compatibility for non-metallic seals used in oilfield equipment operating anywhere in the world. What started with mainly Norwegian or European requests for NORSOK M-710 approved materials has now extended across the globe, making NORSOK into an internationally recognized standard.

NORSOK M-710 – Qualification of non-metallic sealing materials and manufacturers (Rev. 2, Oct. 2001) – requires that all sub- components of oilfield equipment must be approved to stated specifications. Specifically, individual seal materials are rigorously tested and approved based on numerous criteria such as Rapid Gas Decompression (RGD), sour and sweet gas aging, compression set tests, and material property tests.

The testing is done to ensure adequate safety, value adding and cost effectiveness for existing and future petroleum industry developments. The standard defines the requirements for critical non-metallic (polymer) sealing, seat and back up materials for permanent use subsea, including well completion, trees, control systems, wellheads and valves.

The standard also applies to topside valves in critical gas systems. One of the main differences from previous approvals is that all individual components within an assembly must meet and be approved to NORSOK standards, rather than just the complete assembly.

What is Rapid Gas Decompression (RGD)?

Gas or gas mixtures in contact with elastomer surfaces can be absorbed under pressure. At high pressure absorbed gas is in a compressed state. When external pressure is reduced, either rapidly or over a relatively short period of time, the compressed gas rapidly expands within the elastomer. This can lead to crack initiation within the body of the elastomer. These cracks propagate internally and can cause void formation or cracks to appear on the elastomer surface that significantly reduce seal integrity.

Rapid Gas Decompression (RGD) Testing

Three variables are tested: medium, temperature and pressure. Three media options are available (see Table 1); the media selection being dependent on proposed well conditions. Temperatures can be tested at +212°F, +302°F or +392°F / +100°C, +150°C or +200°C.

The material is heated to this temperature progressively and held for 10 minutes. After this, pressures of 2,175 psi, 2,900 psi or 4,351 psi / 15 MPa, 20 MPa, 30 MPa are applied. Exposure to these conditions must be for at least 72 hours.  The sample is then depressurized at a rate of 290-580 psi/min / 2-4 MPa/min, and cooling is only allowed following this. 10 cycles of pressurization and depressurization are applied to the sample, holding pressure for 23-24 hours per cycle.

The sample is then analyzed by microscopy and a rating is applied, summarizing the observed damage to the test sample in terms of number and length of internal cracks visible when the seal is cut into quarters.

Table 1

Test media for EDR testing (From NORSOK Standard M-710)
Sweet / Sour Wells / Low CO2 Sweet / Sour Wells / High CO2 CO2 Injection Wells
3% CO2 , 97% CH4 10% CO2 , 90% CH4 100% CO2

 

Sour & Sweet Gas Aging

Test conditions are simulated to be representative of the seal application environment in both sour and sweet service conditions (Tables 2 & 3 respectively). Three temperatures are selected to accelerate results for extrapolation, all of which are higher than service conditions.

After heating the gas to the required temperature, 1,450 psi / 10 MPa of pressure is applied. Exposure time takes into account the length of time required to reach saturation and is sufficient to allow reliable extrapolation of results.

A minimum of 30 samples are tested. Measurements are taken for sample dimensions, volume and weight prior to exposure. After testing, sample volume and weight are measured again, tensile properties are tested and the sample is visually inspected for damage.

Table 2

Test conditions for sour service conditions (From NORSOK Standard M-710)
Volume % Composition
30 3% CO2 , 2% H2S, 95% CH4
10 Distilled water (conductivity < 5 μS)
60 70% heptane, 20% cyclohexane, 10% toluene


Table 3

Test conditions for sweet service conditions (From NORSOK Standard M-710)
Volume % Composition
30 3% CO2 , 97% CH4
10 Distilled water (conductivity < 5 μS)
60 70% heptane, 20% cyclohexane, 10% toluene

 

Trelleborg Sealing Solutions has one of the largest and most comprehensive selections of fully approved NORSOK M-710 materials on the market. The range includes best-in-class formulae over all material types, designed specifically to meet demanding oilfield conditions.

All of Trelleborg Sealing Solutions NORSOK M-710 approved materials have been involved in rigorous independent tests, undertaken and supervised by Element Materials Technology, a respected independent laboratory in the United Kingdom.

To discuss how NORSOK M-710 approved materials can enhance your design process, contact your local Trelleborg Sealing Solutions Marketing Company.

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